The present invention relates to an alkaline storage battery, for example, a nickel-metal hydride storage battery, nickel-cadmium storage battery, nickel-zinc storage battery and the like, a nickel hydroxide electrode for a positive electrode of the alkaline storage battery and a method for preparing the nickel hydroxide electrode. Especially the invention is characterized as an improved nickel hydroxide electrode for an alkaline storage battery which comprises an active material mainly composed of nickel hydroxide filling pores of a porous sintered substrate which provides a high discharge capacity even if the battery is charged under a high temperature atmosphere.
Conventionally in an alkaline storage battery, of which a nickel-metal hydride storage battery and a nickel-cadmium storage battery are typical examples, a nickel hydroxide electrode for an alkaline storage battery containing nickel hydroxide as an active material is employed as a positive electrode.
As such nickel hydroxide electrode for an alkaline storage battery, a sintered nickel electrode has commonly been used. The sintered nickel electrode is prepared by sintering nickel powder on a punched steel plank as a core to obtain a porous sintered substrate, chemically impregnating the porous sintered substrate with a nickel salt, for example, nickel nitrate or the like, and then treating the substrate with an alkaline solution to convert the nickel salt in the pores of the substrate to nickel hydroxide as an active material filling the pores of porous sintered substrate.
The sintered nickel electrode has an advantage of having excellent charge-discharge characteristics because the sintered substrate has good conductivity and nickel hydroxide powder as an active material and the sintered substrate have good adhesion.
However, an alkaline storage battery having the above described sintered nickel electrode is charged under a high temperature atmosphere and there is a problem that sufficient discharge capacity cannot be obtained because an oxygen overvoltage at the positive electrode becomes low and, in addition to the charge reaction in which nickel hydroxide is oxidized to nickel oxyhydroxide, an oxygen generating reaction occurs.
An object of the present invention is to solve the above-described problem of an alkaline storage battery comprising a nickel hydroxide electrode that contains nickel hydroxide as a main active material provided in the pores of a porous sintered substrate.
More specifically, the present invention provides an improved nickel hydroxide electrode for an alkaline storage battery that contains nickel hydroxide as a main active material in the pores of a porous sintered substrate and makes it possible to have a high discharge capacity when the alkaline storage battery is charged at a high temperature.
The present invention provides a nickel hydroxide electrode for an alkaline storage battery having a titanium hydroxide on the surface of nickel hydroxide as a main active material filling the pores of a sintered substrate. As a titanium hydroxide, titanium hydroxide (Ti(OH)4), titanic acid (H4TiO4) or the like can be exemplified.
The present invention also provides an alkaline storage battery comprising, as a positive electrode, the nickel hydroxide electrode that comprises titanium hydroxide on the surface of a nickel hydroxide provided in the pores of a sintered substrate.